io: add Send / Sync impls for ReadHalf / WriteHalf (#1525)

tokio-io/tests/split.rs

@@ -1,4 +1,5 @@
 use tokio::io::{split, AsyncRead, AsyncWrite};
+use tokio_io::split::{ReadHalf, WriteHalf};
 
 use std::io;
 use std::pin::Pin;
@@ -34,6 +35,14 @@ impl AsyncWrite for RW {
     }
 }
 
+#[test]
+fn is_send_and_sync() {
+    fn assert_bound<T: Send + Sync>() {}
+
+    assert_bound::<ReadHalf<RW>>();
+    assert_bound::<WriteHalf<RW>>();
+}
+
 #[test]
 fn unsplit_ok() {
     let (r, w) = split(RW);